The tinker is a melee, heavy armour wearing mad scientist healer, that uses his abilities to generate his primary resource Bio-Energy.
As long as you have above 0 energy, your backpack activates and begins sending out healing beams called the Auto-Stitch Protocol to nearby allies (prioritizing low health), greatly increasing in frequency the higher your energy, but draining energy faster the more you have.
The core gameplay loop would be maintaining your energy as high as you can when healing is needed, using effects that boost energy generation, slow energy drain, or just give you energy flat out.
Core heals would be spells like Med-Pack launcher, that send out a healing projectile, dealing flat healing and generating bio-energy, with more generated the lower health of the target. AOE spells like Systems Boost, which would instantly generate 50% energy and reduce energy drain rate for a short time.
Melee abilities like Shock Wrench with no cd would generate a small amount of bio energy, while capacitor smash would be a windup melee smash that generates extra energy.
You would of course have a healing turret, every heal tick would generate a small amount of energy, if all allies are at full health the turret instead would attack enemies.
An example of a CD would be Turret Overclock, that would increase the tick rate, healing amount, and energy generation of your turret.
Your ult would be "Emergency Construct Swarm" which would instantly deploy 3-4 additional turrets, all the turrets would contribute healing, damage, and energy.